In recent years, materials used for dental restorations have comprised principally methacrylate polymers. Typical of these polymeric substances are the acrylic resinous materials disclosed in U.S. Pat. No. 3,066,112, No. 3,179,623, No. 3,194,784, No. 3,751,399 and No. 3,926,906. Especially noteworthy is the compound which is the condensation product of bisphenol A and glycidyl methacrylate, 2,2'-bis [4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (hereinafter abbreviated to "BIS-GMA"). Other methacrylate polymers, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate, are also in general use as diluents. Polyurethanedimethacrylate is also used as a principal polymer in dental restorative materials of this type. Since BIS-GMA is highly viscous at room temperature, it is generally diluted with a monomer having a lower viscosity such as the aforementioned alkylene glycols or other compatible materials, including trimethylol propyl trimethacrylate, 1,6-hexanediol dimethacrylate, 1,3-butanediol dimethacrylate, and the like.
When these acrylic resinous materials were first developed, they were used unfilled for dental restorative purposes. However, because acrylic materials exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion for the tooth structure, these unfilled substances soon proved to be less than satisfactory. The disparity in thermal expansion, coupled with high shrinkage upon polymerization, resulted in poor marginal adaptability and ultimately led to secondary decay. Furthermore, the wear and abrasion characteristics and the overall physical, mechanical and optical properties of these unfilled acrylic resinous materials were quite poor. Thus, from the outset, composite dental restorative materials containing these methacrylate resins and fillers were developed. The fillers are generally inorganic filler materials based on silica, silicate glass, or quartz.
Over the years, there have been a number of refinements in the resin matrix component, in the filler component, and in the other additives--notably antioxidants, ultraviolet absorbers, polymerization initiators, polymerization accelerators, etc.--in dental restorative materials. There are now available materials which exhibit high diametral tensile strength, excellent optical properties and polishability, and low water absorption while, at the same time, complying with all of the requirements specified in ADA Specification No. 27 for direct filling resins. Particularly suitable restorative materials are the new compositions having improved inorganic filler materials such as those disclosed in my U.S. Pat. No. 4,547,531, disclosing self-curing 2-component compositions, and U.S. Pat. No. 4,544,359, disclosing visible light curable compositions.
All of these dental restorative materials are required to adhere permanently to the tooth structure. Generally, the tooth surface is treated with an acid such as 30-50 wt. % orthophosphoric acid, which etches the enamel tooth surface and exposes enamel rods in honeycomb prismatic structure thereon, whereby adhesion of the cured polymeric material is improved via micromechanical interlocking. In addition to this process of etching, the prior art teaches the use of various additives and improved monomeric mixtures which are designed to provide improved adhesion.
Although the acid etching technique by itself or coupled with modification of the resinous material to increase adhesive capability has been beneficial in effecting the bonding of dental restorative materials to tooth enamel, there has heretofore been no completely satisfactory process for adhering such restorative materials to dentin. Acid etching is not suitable for bonding dental restorative materials to dentin because the tubular structure of dentin provides passageways to the tooth pulp. The acid can cause great inflammation and pain to the patient and ultimately lead to pulpal necrosis. Furthermore, the high percentage of organic (protein) material in the dentin results in a lower degree of adhesion as compared with enamel.
There has recently been proposed a method for improving adhesion of dental composite materials to dentin surfaces which involves the successive application of (a) an acidic salt such as ferric oxalate or ferric citrate, (b) the adduct of N-(p-tolyl)-glycine and glycidyl methacrylate, the addition reaction product of N-phenylglycine and glycidyl methacrylate or N-phenylglycine itself, and (c) the addition reaction product of pyromellitic acid dianhydride and 2-hydroxyethylmethacrylate, the addition reaction product of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 2-hydroxyethylmethacrylate, or 4-methacryloxyethyltrimellitic anhydride. This multi-step process has, however, not proved satisfactory.
In addition to much desired improvements in dentin bonding systems, it is also desirable to attain improved bonding to other dental surfaces, such as enamel, alloy-substrates and, particularly porcelain.
Despite recent advances in the development of filled dental restorative materials which have led to composites having higher resistance to abrasion, better handling characteristics, and more satisfactory visual appearance, there remains considerable room for improvement in these areas. Specifically desired are improved filled compositions for use as crown and bridge materials, denture-base materials, luting agents or cements and orthodontic appliance materials and sealants.
Accordingly, it is one primary object of this invention to provide improved dental adhesive materials for bonding to dentin, enamel, metallic alloys and porcelain.
It is another primary object of this invention to provide improved filled compositions for use as luting agents, denture-base materials, orthodontic materials and sealants, crown and bridge materials and other dental restorative materials.
It is a further object of this invention to provide a method for bonding a dental restorative material to a properly prepared tooth surface including dentin, enamel metallic alloys and porcelain.
Other objects include the provision of a dentin bonding system which employs a non-irritating pretreatment to yield a proper surface for application of the dental adhesive.
Still another object is to provide improved a dental adhesive which is particularly suitable for bonding to a properly prepared dentin surface. Other objects of this invention will become apparent from the following specification.